Optical waveguide device and method of manufacture thereof

ABSTRACT

An optical waveguide device according to the invention is provided with a substrate ( 271 ), a metal layer ( 272 ) arranged on the substrate ( 271 ), a plurality of claddings ( 262 ) arranged on the metal layer ( 207 ) via grooves ( 205 ), cores ( 202 ) arranged in the claddings ( 262 ) for transmitting lights, optical waveguides ( 201 ) having optically non-transmissive material ( 291 ) coating the insides of the grooves ( 205 ) and optically non-transmissive and electrically insulating material ( 273 ) coating the top faces of the claddings ( 262 ), and light receiving elements ( 203 ) for receiving lights emitted from the end faces of the cores ( 202 ). In an optical waveguide device according to the invention, dents ( 204 ) in which the end faces of the cores are exposed ( 202 ) may be formed, the inside faces of the dents ( 204 ) being coated with optically non-transmissive material except where the end faces of the cores are exposed. Also, in an optical waveguide device according to the invention, the cores ( 202 ) and the light receiving elements ( 203 ) may be paired and provided in a plurality each, and the light receiving elements ( 203 ) may be divided into odd-number and even-number groups, which are arranged with some spacing between them, the odd-number and even-number groups being blocked from each other by optically non-transmissive material ( 301 ).

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 10/403,320filed Mar. 28, 2003 entitled OPTICAL WAVEGUIDE DEVICE AND METHOD OFMANUFACTURE THEREOF, which claims the benefit of Japanese ApplicationNo. 90576/2002 filed on Mar. 28, 2002, the contents of which areincorporated by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical waveguide device and amethod of manufacture thereof, and more particularly to an opticalwaveguide device enabled to eliminate or reduce the influences of straylights and a method of manufacture thereof.

2. Description of the Related Art

Communication technology is advancing dramatically, driven by thedevelopment of the Internet among other factors. Along with that,optical devices are required rapidly to achieve high performance andminiaturization. In order to realize this requirement, hybrid mountingof optical devices is performed briskly. One example is an opticaldevice in which optical functional elements such as laser diodes (LDs),photodiodes (PDs) and optical amplifiers for receiving optical signalsare hybrid-mounted on a planar lightwave circuit (PLC) chip.

In addition recently, in compliance with the demand for large increasingcapacity in communication capacity, wavelength division multiplexing(WDM) communication is developing. For this purpose, it is frequentlyattempted to mount components for a plurality of channels on a singleoptical waveguide substrate. As an example, a plurality of lightreceiving elements are hybrid-mounted on an arrayed waveguide grating(AWG) as a trial production as disclosed in U.S. Pat. No. 5,680,236(OECC2000 Tech Digest, July 2000, 12C2-2). In such hybrid mounting,optical functional elements are fixed to an end face or the top face ofan optical waveguide substrate by soldering or with adhesive. As forsuch integrated structure, lights leaking from each part components areeasy to enter into other part components as stray lights. This resultsin a trouble of giving rise to optical crosstalk. There are a number ofknown measures to prevent such optical crosstalk from increasing. Forinstance, where there are multiple channels, it is a general practice toexpand the spacing between optical waveguides or components to bemounted in a fan-out structure.

FIG. 12 illustrates the structure of an optical device proposed toreduce optical crosstalk according to the prior art. On the opticalwaveguide substrate 101 of an optical waveguide device 100 are formed aplurality of optical waveguides 102 ₁, 102 ₂, . . . 102 ^(N). At one endof each of the optical waveguides 102 ₁, 102 ₂, . . . 102 ^(N) isarranged a matching one of light receiving elements 103 ₁, 103 ₂, . . .103 ^(N) for the respective channels. Lights being inputted from theleft ends of, and being transmitted in, the optical waveguides arereceived by the respective light receiving elements. In this proposedconfiguration, the spacing between the optical waveguides 102 ₁, 102 ₂,. . . 102 ^(N) is radially expanded as they approach the light receivingelements 103 ₁, 103 ₂, . . . 103 ^(N). This arrangement makes itpossible to expand the spacing between the light receiving elements 103₁, 103 ₂, . . . 103 ^(N). As a result, stray lights from the opticalwaveguides having failed to be inputted into the light receivingelements can be prevented from being inputted into light receivingelements of other channels, and optical crosstalk can be therebyreduced. However, the structure according to the prior art shown in FIG.12 has its own problem that the optical waveguide substrate has to beenlarged with an increase in the number of channels because the mountingwidth of light receiving elements expands. For this reason, the numberof optical waveguide substrates that can be cut out of a wafer isreduced, and the cost is accordingly increased. There is another problemthat the package to mount this optical waveguide substrate cannot beminiaturized.

Also, as shown in FIG. 12, it is often impossible to achieve asufficient effect by simply expanding the spacing between components.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an optical waveguidedevice which is capable of reducing optical crosstalk without having toexpand the spacing between the plurality of optical functional elementsmounted on an optical waveguide substrate and a method of manufacturethereof.

An optical waveguide device according to the invention is provided withoptical waveguides whose cores are arranged in a plurality in claddingsformed on a substrate and light receiving elements for receiving lightsemitted from these cores respectively, wherein a metal layer is formedbetween the substrate and the claddings, and grooves are formed betweenthe cores by removing of the claddings. The insides of these grooves arecoated with optically non-transmissive material, and the top faces ofthe claddings are coated with optically non-transmissive andelectrically insulating material. Furthermore, the opticallynon-transmissive material is coated by a film forming process, and theoptically non-transmissive and electrically insulating material iscoated by painting. Optical paths from the end faces of the cores to thelight receiving faces and the surroundings of the light receivingelements are filled with optically transmissive and electricallyinsulating material, whose top parts are either coated with opticallytransmissive and electrically insulating material or blocked from oneanother.

In the optical waveguides, there are formed dents in which the end facesof the plurality of cores are exposed, and the insides of the dents arecoated with optically non-transmissive material except on the faceswhere the end faces of the cores are exposed. This coating of theinsides of the dents is coated by a film formation process in adirection slanted relative to the top faces of the claddings.Furthermore, the dents are provided with mirrors to reflect lightsemitted from the end faces of the cores and to make to input them intothe light receiving light receiving faces of the light receivingelements.

In addition, the light receiving elements are divided into odd-numberand even-number groups, which are arranged with some spacing betweenthem and blocked by optically non-transmissive material.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawingswherein:

FIG. 1 shows a plan of an optical waveguide device, which is a firstpreferred embodiment of the invention;

FIG. 2 shows a vertical section of the surroundings of first throughthird optical waveguides of FIG. 1;

FIGS. 3(a) through 3(d) show vertical sections of the manufacturingprocess of the surroundings of first through third optical waveguides ofFIG. 1;

FIG. 4 shows a plan of a substrate of the optical waveguide device whichis the first preferred embodiment of the invention;

FIG. 5 shows a plan of the surroundings of the mounting of lightreceiving elements of FIG. 4;

FIG. 6 shows a cross section in the A-A direction in FIG. 5;

FIG. 7 show cross sections of the process of producing the opticalwaveguide device, which is the first embodiment of the invention; FIG. 7(a) showing the state before film formation and FIGS. 7(b) and 7(c)showing the states during film formation by different methods;

FIG. 8 show vertical sections of the surroundings of light receivingelements of the optical waveguide device, which is the first embodimentof the invention; FIG. 8(a) showing a first optical blocking structureand FIG. 8(b), a second optical blocking structure;

FIG. 9 show plans of modified versions of the structure around a dent inthe optical waveguide device, which is the first embodiment of theinvention;

FIG. 10 shows a cross section of the configuration of an opticalwaveguide device, which is a second preferred embodiment of theinvention;

FIG. 11 shows a plan of the configuration of an optical waveguidedevice, which is a third preferred embodiment of the invention; and

FIG. 12 shows a plan of the configuration of the optical deviceaccording to the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The basic configuration and operating principle of the optical waveguidedevice according to the invention will be described below.

FIG. 1 illustrates the substrate configuration of the optical waveguidedevice according to the invention. In the optical waveguide substrate201 of an optical waveguide device 200 according to the invention, firstthrough Nth cores (cores of optical waveguides) 202 ₁, 202 ₂, . . . 202_(N) are formed in parallel to one another. At the righthand ends ofthese first through Nth cores 202 ₁, 202 ₂, . . . 202 _(N) arerespectively arranged first through Nth light receiving elements 203 ₁,203 ₂, . . . 203 _(N). In intermediate positions of the first throughNth cores 202 ₁, 202 ₂, . . . 202 _(N) and outside the first and Nthcores 202 ₁ and 202 _(N), and in parallel to them, are arrangedinterception grooves 205 ₁ through 205 _(N+1). The inside faces of theseinterception grooves 205 ₁ through 205 _(N+1) are coated with opticalblocking material 291.

FIG. 2 shows a cross section of the first through third cores and theinterception grooves around, cut in a direction at a right angle to thetransmitting direction of signal light. The structure is such that theinterception grooves 205 ₁, 205 ₂, 205 ₃ and 205 ₄ are sequentiallyarranged in order on both sides of one of the first through third cores202 ₁, 202 ₂ and 202 ₃ between them. The inside faces of theseinterception grooves 205 ₁ through 205 ₄ are coated with the opticalblocking material 291. Between a substrate layer 271 and claddings 262is formed a metal layer 272, and on the top face of each of thecladdings 262 is stacked optical blocking material 273 consisting ofoptical blocking resin. This optical blocking material 273 is aninsulator so that, even if it comes into contact with an electrode (notshown), no short circuiting may occur, and its equivalent refractiveindex is close to that of the claddings or value the above that (thecladdings of the optical waveguides) so that lights leaking to thecladdings can be effectively absorbed. As a result, lights leaking tothe claddings can be readily absorbed by the optical blocking materialwithout being reflected by the boundary face with the optical blockingmaterial. Thus each of the claddings 262 is optically independent of thematching one of the cores 202 ₁ through 202 ₃. For this reason, nolights leaking from the cores 202 ₁ through 202 ₃ to the claddings 262leak out of the claddings 262. Therefore, stray lights can be preventedfrom entering into any other channel and thereby worsening opticalcrosstalk. Furthermore, since the inside faces of the grooves areprocess-formed, they afford high productivity and can be adequatelycoated even if the grooves are very fine. On the other hand, since thetop faces of the claddings are coated with insulating material, even ifthey come into contact with an electrode pattern or the like, no shortcircuiting can occur. Moreover, because only the top faces of thecladdings are coated, highly viscous coating material can be used. Inaddition, the fourth through Nth cores and their surroundings areconfigured in the same way as those illustrated in FIG. 2. FIGS. 3illustrate a manufacturing process of the parts shown in FIG. 2.

FIG. 3(a) illustrates a state in which the metal layer 272 is formedover the top face of the substrate layer 271, the claddings 262 and thecores 202 ₁, 202 ₂ and 202 ₃ are formed still on it, and maskingmaterial 281 having a prescribed width is formed over the top faces ofthe claddings 262 so as to cover the cores 202 ₁, 202 ₂ and 202 ₃. Themasking material 281 consists of metal or resist. As shown in FIG. 3(b),using a reactive ion etching (RIE) apparatus, the interception grooves205 ₁, 205 ₂, 205 ₃ and 205 ₄ are formed.

Then, as shown in FIG. 3(c), the grooves are coated inside with theoptical blocking material 291 by vapor deposition, sputtering orotherwise.

Further as shown in FIG. 3(d), the masking material 281 is removed, andthe optical blocking material 273 is adhered, resulting in therealization of the structure illustrated in FIG. 2.

Incidentally, instead of coating the top faces of the claddings 262 withthe optical blocking material, the masking material 281 may be removedafter the step shown in FIG. 3(b), and the inside faces of theinterception grooves 205 ₁ through 205 ₄ and the top faces of thecladdings 262 may be formed simultaneously of the optical blockingmaterial 291.

In addition, the optical blocking material 291 can be metal, metal-dopedglass or ceramic. The optical blocking material 273 may be ceramic,metal-doped glass or resin. The preferable metal is Au, Pt or Cr interms of coat stability, or Ti, Pt, Ni or W in terms of low opticaltransmissivity. Some other metal or alloy may also fit the purpose.Suitable ceramics include silicon carbide, silicon nitride, or the like.Preferable metal-doped glasses include, for instance, doped quartz withhigh Ti and Ge contains. A suitable resin may be epoxy resin, or thelike.

FIG. 4 illustrates the optical waveguide substrate of the opticalwaveguide device according to the invention. In the optical waveguidesubstrate 201 of the optical waveguide 200 according to the invention,first through Nth dents 204 ₁, 204 ₂, . . . 204 _(N) are formed in thepositions where the first through Nth light receiving elements 203 ₁,203 ₂, . . . 203 _(N) are formed so as to expose the end faces of thecores respectively. In these dents 204 ₁, 204 ₂, . . . 204 _(N) aremounted mirrors 222 ₁, 222 ₂, . . . 222 _(N) to reflect lights emittedfrom the ends of the cores 202 ₁, 202 ₂, . . . 202 _(N) toward the lightreceiving faces of the light receiving elements 203 ₁, 203 ₂, . . . 203_(N).

FIG. 5 shows an enlarged view of the surroundings of the position inwhich the first light receiving elements 203 ₁ is fitted to the opticalwaveguide substrate 201, and FIG. 6, a cross section in the A-Adirection in FIG. 5. The positions in which the second through Nth lightreceiving elements 203 ₂ . . . 203 _(N) are fitted are structured in thesame way as the position in which the first light receiving elements 203₁ is fitted.

As shown in FIG. 5, the pedestals 211 through 214 are formed on theoptical waveguide substrate 201 in the position where the first lightreceiving element 203 ₁ is mounted. These pedestals 211 through 214, asillustrated in FIG. 6, are formed convexly on the top face of theoptical waveguide substrate 201.

The first light receiving element 203 ₁ is fixed over these pedestals211 through 214. The pedestals 211 through 214 are also used asterminals for taking electrical signals out of the first light receivingelement 203 ₁. An end face 221 of the first core 202 ₁ is exposed on awall surface 227 of the dent 204 ₁. On the bottom face of the dent 204 ₁is installed the mirror 222. Further as shown in FIG. 5, on the righthand side of the dent 204 ₁ is formed a groove 224 by extending thedent. The righthand end 225 of the groove 224 extends as long as toslightly expose from the righthand end of the first light receivingelement 203 ₁ which covers the groove. Also, over the inside face of thedent 204 ₁, except the wall surface 227, is formed a film of opticalblocking material 226. A film of optical blocking material 226 is alsoformed over the inside face of the groove 224. The pedestals 211 through214 are formed of the same material as the first core 202 ₁ over thesurface of the optical waveguide substrate 201. Incidentally, it is alsopossible to form the pedestals 211 through 214 at a separate step.

FIGS. 7 illustrate the process of forming a film of optical blockingmaterial over all the faces but one of each dent. Here is schematicallyshown the dent 204 ₁ illustrated in FIG. 5 and FIG. 6.

FIG. 7(a) shows a section of the dent 204 ₁ before the optical blockingmaterial film is formed. On the wall surface 227 is exposed an end faceof the first core 202 ₁. In this state, the optical blocking material isvapor-deposited into the dent 204 ₁ at an angle indicated by an arrow231 as shown in FIG. 7(b). The angle q formed by the arrow 231 to thedirection normal to the top face of the optical waveguide substrate 201is supposed to be 15 degrees, though this angle q can be varied from 0degree (perpendicular) to 90 degrees (horizontal) as desired. Thisenables the film of optical blocking material to be vapor-deposited onall the faces of the dent 204 ₁ but the wall surface 227. It is alsopossible to similarly form the film optical blocking material bysputtering.

The reason why the wall surface 227 is excluded from vapor deposition isthat obstruction of light emission from the first core 202 ₁ can bethereby prevented. The formation of the film of optical blockingmaterial over all the other faces than the wall surface 227 is, asillustrated in FIG. 6, to prevent lights not being inputted on the firstlight receiving element 203 ₁, out of the lights being inputted from theend face 221 of the first core 202 ₁ on the dent 204 ₁, from becomingstray lights and being inputted into other dents to affect otherchannels. The film of optical blocking material formed over the dent 204₁ is made of metal or some other light-absorptive material. The metalcan be chosen from Au, Pt, Cr, Ti, Pt, Ni, W and alloys, and availablelight-absorptive materials include ceramics, such as silicon carbide andsilicon nitride, and glasses heavily doped with metals such as Ti andGe.

FIG. 7(c) illustrates another method of forming a film of opticalblocking material in the dent. FIG. 7(b) shows vapor deposition in aslanted direction. On the other hand, FIG. 7(c) illustrates vapordeposition over the other faces than the wall surface 227 by arranging amasking member 241 over the wall surface 227.

In this embodiment of the invention, the film is vapor-deposited overthe dent 204 ₁ and the groove 224 by the method shown in FIG. 7,followed by installation of the mirror 222 shown in FIG. 6 on the bottomface of the dent 204 ₁. Use of gold both for the film to bevapor-deposited and the mirror also provides the vapor-deposited gold toperform the function of fixing the mirror securely. In addition, it isalso possible to form the mirror surface and the inside faces of thedent 204 ₁ by arranging on the bottom face of the dent 204 ₁ in advancea projection which would eventually constitute the mirror and thenvapor-depositing metal with a high reflection factor, such as gold.

After forming the optical blocking material film 226 over the dent 204 ₁and installing the mirror 222, the first light receiving element 203 ₁is fixed to the pedestals 211 through 214 as shown in FIG. 6.

In addition, a prescribed one of the pedestals 211 through 214 isconnected to an electrode pattern (not shown) on the optical waveguidesubstrate 201, and the light reception output of the first lightreceiving element 203 ₁ can be supplied to circuit portions (not shown)via this electrode pattern.

FIG. 8 show vertical sections of the surroundings of the dent 204 ₁ inthe embodiment of the invention after being filled with resin. After thefirst light receiving element 203 ₁ is fitted to the optical waveguidesubstrate 201 as stated above, resin 242 having transmissivity in thewavelength range of signal lights is injected into the dent 204 ₁ fromthe groove 224 shown in FIG. 5 and FIG. 6. Then the inside of the dent204 ₁ is filled with the resin 242 until the top of the first lightreceiving element 203 ₁ is covered with it. As shown in FIG. 8(a), thetop of this resin 242 is further covered with optical blocking resin 243having transmissivity in the wavelength range of no signal light.

The resin 242 is an insulator so that no short circuiting can occur evenif it comes into contact with the electrode portion of the lightreceiving element 203 ₁ or the pedestal connected to the electrodepattern. The optical blocking resin 243 also is an insulator so that noshort circuiting can occur even if it comes into contact with anelectrode pattern (not shown) formed on the claddings. The resin 242 isfilled in an island state, in which the first through Nth the lightreceiving elements 203 ₁, 203 ₂, . . . 203 _(N) are independent of oneanother as shown in FIG. 1, and the top of each is covered with theoptical blocking resin 243. This arrangement makes it possible toeffectively reduce optical crosstalk due to stray lights which are aptto occur in a structure in which light receiving elements are arrayedadjoining each other. Incidentally, silicon resin is used as the resin242, and epoxy resin or the like, as the resin 243.

FIG. 8(b) shows another structure for preventing optical crosstalk fromarising. In the structure shown in FIG. 8(a), the optical blocking resin243 is applied so as to cover the top face of the resin 242. On theother hand, in the structure shown in FIG. 8(b), a wall 251 consistingof optical blocking resin is arranged between the light receivingelements 203 ₁ and 203 ₂. This disposition can prevent lights leakingout of gaps between the light receiving elements 203 ₁ and 203 ₂ and theoptical waveguide substrate 201 from entering into any other channel.Incidentally, epoxy resin or the like is used for the wall 251.

As described above, in this embodiment of the invention, stray lights innot only the area of the first through Nth light receiving elements 203₁, 203 ₂, . . . 203 _(N) but also in that of the first through Nth cores202 ₁, 202 ₂, . . . 202 _(N) are provided against as shown in FIG. 4. Asa result, even if the degree of integration of the light receivingelements 203 over the optical waveguide 200 increases, optical crosstalkbetween different wavelengths or between channels can be effectivelyreduced. Therefore, the optical waveguide 200 can be enhanced in thedegree of integration and improved in performance at the same time. Thismakes it possible to reduce the size, and accordingly the cost, ofoptical waveguide devices.

FIG. 9 illustrate modified versions of the structure around a dentaccording to the invention. In one version shown in FIG. 9(a),projections together forming a V shape are provided, one on each side,at an end face of the core 202 on the wall surface 227 where the endface of the core 202 is exposed. If film formation in the slantedfashion described with reference to FIG. 7 is applied to such a wallsurface 227A, a film of optical blocking material will be formed overeach of two faces 227AA and 227AB. In this way, the two faces 227AA and227AB can block stray lights 401 and 402, which would otherwise inputinto a dent 204A, from doing so. As a result, the detection output ofthe light receiving elements 203 (not shown in this drawing) can beprevented from being affected by stray lights arriving from otherchannels or elsewhere.

In the other version shown in FIG. 9(b), reflective stubs 411 and 412are arranged in positions which are located between the wall surface227, where the end face of the core 202 is exposed, and the mirror 222and where lights being inputted from elsewhere than the end face of thecore 202 can be avoided. These reflective stubs 411 and 412, too, areformed of films of optical blocking material in the slanted fashiondescribed with reference to FIG. 7 on the side opposite the wall surface227. The stray lights 401 and 402 which would otherwise input on thedent 204B from elsewhere than the core 202 are blocked by thesereflective stubs. As a result, adverse effects on the light receivingelements 203 (not shown in this drawing) can be suppressed.

FIG. 10 shows a cross section of the surroundings of a dent provided inan optical waveguide device as a second preferred embodiment of theinvention. In FIG. 10, the same constituent parts as in FIG. 6 aredenoted by respectively the same reference signs, and their descriptionwill be dispensed with. A dent 501 in this second embodiment, formed inthe same fashion as the dent 204 ₁ in the foregoing embodiment (see FIG.6), accommodates no mirror. A photodiode 502 is firmly fitted to thebottom face of the dent 501 as a light receiving element. The photodiode502 directly receives light emitted from the end face 221 of the firstcore 202 ₁. The output current of the photodiode 502 is connected to anelectrode pattern (not shown) on the surface of the optical waveguidesubstrate via wires 503 and 504 connected to the top face of thephotodiode 502. In this second embodiment of the invention, too, a film226 of optical blocking material is formed over the inside faces of thedent 501 other than the face containing the end face 221 of the firstcore 202 ₁. This film can be formed by the method of film formationdescribed with reference to FIG. 7. By using metal as the material ofthe film to be formed on the bottom face of the dent, at least one ofthe electrodes of the photodiode 502 can be connected via the metallicfilm 226 on the bottom face of the dent. It is also possible to dispensewith the electrode pattern on the surface of the optical waveguidesubstrate by mounting a photodiode (not shown) fixed to the subcarrier.

Although in the embodiments of the invention so far described, theoptical blocking material film 226 is not formed all over the wallsurface 227 including the end face 221 of the core, it is also possibleto form the optical blocking material film 226 all over the wall surface227 with only the end face 221 of the core being excluded. This wouldresult in a further reduction of optical crosstalk. FIG. 11 illustratesthe configuration of an optical waveguide device as a third preferredembodiment of the invention. In FIG. 11, the same constituent parts asin FIG. 1 are denoted by respectively the same reference signs, andtheir description will be dispensed with. In this optical waveguide200A, odd-number (such as first, third and so forth) light receivingelements 203 ₁, 203 ₃, . . . 203 ₇ on the optical waveguide substrate201A are arranged in one column, and even-number (such as second, fourthand so forth) light receiving elements 203 ₂, 203 ₄, . . . 203 ₈ arearranged on another column. These two columns are apart from each otherat a prescribed distance L. This zigzag arrangement of the first througheighth light receiving elements 203 ₁, 203 ₂, . . . 203 ₈ doubles thelateral spacing of the light receiving elements 203 and thereby reducesoptical crosstalk.

This point will now be described as it relates to FIG. 12. Generallyspeaking, in trying to reduce optical crosstalk in arrayed multi-channeloptical waveguides with light receiving function, the optical waveguidesare fanned out by using curved optical waveguides as shown in FIG. 12.The square measure increment of the optical waveguide substrate 101(FIG. 12) in this configuration will be considered below. In thefollowing mathematical expressions, the spacing between the opticalwaveguides before fan-out is represented by P1; that after fan-out, byP0; the number of the optical waveguides, by N; and the minimum radiusof curvature, by R.

In this case, the width increment of the optical waveguide substrate101, represented by h₁₀₁, can be expressed in Equation (1) below.h ₁₀₁=(P ₀ −P ₁)*(N−1)   (1)

The width increment of the optical waveguide substrate 101, representedby w₁₀₁, can be expressed in Equation (2) below.w ₁₀₁={square root}(h ₁₀₁ R/2−h ₁₀₁ ²/8)   (2)

On the other hand, the light receiving elements are supposed to bearranged in a zigzag fashion as in this second embodiment. In thefollowing mathematical expressions, the spacing between the columns isrepresented by L; the width of the optical waveguide substrate 201A inthe zigzag arrangement, by h₂₀₁; and the length increment, by w₂₀₁. Thewidth h₂₀₁ can be expressed in Equation (3), and the length incrementw₂₀₁, by Equation (4) below.h ₂₀₁ =P ₁*(N−1)   (3)w ₂₀₁=(N−1)*P ₁ *L   (4)

On the basis of the foregoing, a case in which the distance to thenearest light receiving element (P₀, L) is extended to a desired lengthis supposed. By using the zigzag arrangement under a condition that thesquare measure increment (L*h₂₀₁) of the optical waveguide substrate201A be smaller than the square measure increment attributable to thefan-out ((h₂₀₁+h₁₀₁)*w₁₀₁), the square measure of the optical waveguidesubstrate 201A can be made smaller than that of the optical waveguidesubstrate 101. Furthermore, an optical blocking member 301 is applied ina strip shape on the top face of the optical waveguide substrate 201Abetween the column of the even-number light receiving elements 203 ₂,203 ₄, . . . 203 ₈ and that of the odd-number light receiving elements203 ₁, 203 ₃, . . . 203 ₇. This enables lights leaking from one columnof light receiving elements to the other column of light receivingelements to be significantly reduced. Epoxy resin or the like is usedfor this optical blocking member 301. It is possible to further reduceoptical crosstalk in the optical waveguide 200A by additionally usingthe measures against stray lights described with reference to theearlier embodiments. This makes possible a high degree of integrationand a size reduction to achieve a cost saving of the optical waveguidedevice. Increasing the number of columns would enable an even higherdegree of integration to be attained.

As hitherto described, according to the present invention, signal lightsbetween channels can be separated on a cladding-by-cladding basis. Thisenables lights leaking from cores to be prevented from entering intoother cores or other light receiving elements, and accordingly makespossible a reduction in optical crosstalk. Furthermore, since thecladdings are covered on the top face with electrically insulatingmaterial according to the invention. For this reason, even if they comeinto contact with an electrode pattern or electronic part, no shortcircuiting can occur. Therefore, it is made possible to mount anelectrode pattern and/or electronic parts over the top face of thecladdings and thereby to effectively utilize the top face space of thecladdings. Also, according to the invention, as the groove inside facescan be coated in the film formation process, even very fine grooves canbe coated. It is further possible to coat a plurality of grooves at thesame time and thereby to reduce the number of manufacturing man-hoursrequired. For the reasons cited so far, the invention makes it possibleto improve performance against optical crosstalk, enhance the degree ofintegration of components, reduce the size of the optical waveguidedevice, shorten the manufacturing process and correspondingly save thecost.

Furthermore, according to the invention, as dents are provided in theoptical waveguide substrate to receive lights from cores and coatedinside with optical blocking material, light leaks from the dents toother channels can be restrained. Therefore, the light receiving sectionalso contributes to preventing optical crosstalk from worsening.

Moreover, as the insides of the dents are coated with films formed in aslanted fashion according to the invention, a plurality of dents can becoated at the same time and in a simple process.

Also, according to the invention, optical paths are protected by fillingthe dents with optically transmissive material, which is coated withoptical blocking material to prevent stray lights from leaking out.Since this optical blocking material is electrically insulating, itscontact with an electrode pattern or the like would not invite shortcircuiting. Therefore, the degree of integration of components can beenhanced. Incidentally, arrangement of this optical blocking materialbetween the light receiving elements, instead of coating the top facesof each light receiving element with it, would provide the same effect.Furthermore, according to the invention, the zigzag arrangement ofodd-number and even-number light receiving elements can double thespacing between adjacent light receiving elements and thereby reduceoptical crosstalk. Moreover, the arrangement of optical blockingmaterial between the odd-number and even-number columns according to theinvention can further contribute to optical crosstalk reduction.

While the invention has been described with reference to certainpreferred embodiments thereof, it is to be understood that the subjectmatter encompassed by this invention is not to be limited to thosespecific embodiments. Instead, it is intended for the subject matter ofthe invention to include all such alternatives, modifications andequivalents as can be included within the spirit and scope of thefollowing claims.

1. An optical waveguide device, a substrate, a metal layer arranged onsaid substrate, a plurality of claddings arranged on said metal layervia grooves, a core, arranged in each of said plurality of thecladdings, for transmitting lights, optically non-transmissive materialcoating the insides of said grooves, and optically non-transmissive andelectrically insulating material coating the top faces of saidcladdings.
 2. The optical waveguide device, as claimed in claim 1,wherein: said optical waveguide device is further provided with lightreceiving elements for receiving lights emitted from the end faces ofsaid cores.
 3. The optical waveguide device, as claimed in claim 2,wherein: said claddings, said cores and said light receiving elementsare paired and provided in a plurality each.
 4. The optical waveguidedevice, as claimed in claim 3, wherein: said plurality of lightreceiving elements are divided into odd-number and even-number groups,which are arranged with some spacing between them, and said odd-numberand said even-number groups are blocked by said opticallynon-transmissive material.